Hydroperoxides

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Hydroperoxides
General structure of hydroperoxides. R is an organic residue.
R is an organyl group . The functional group is marked in blue .

Hydroperoxides are a class of organic chemical compounds with the general structure R – O – OH, where R is a carbon-containing radical.

Extraction and presentation

Hydroperoxides are mostly formed in auto- oxidation processes (self-oxidation) through the reaction of organic compounds with atmospheric oxygen or through the reaction of organometallic compounds (e.g. Grignard compounds ) with oxygen. The formula shows the light-induced mechanism of hydroperoxide formation using the example of diethyl ether hydroperoxide ("ether peroxide" formation):

Reaction mechanism for the formation of an ether peroxide

The diethyl ether radical initially formed by exposure to light reacts with oxygen to form the ether peroxide radical, which reacts with another molecule of diethyl ether to form diethyl ether hydroperoxide and a diethyl ether radical. Since a new diethyl ether radical is created with each conversion cycle, a chain reaction occurs as long as oxygen is still present. Photooxygenations of alkenes with at least one hydrogen atom in the allyl position lead to hydroperoxides.

For n -alkanes, the reaction with atmospheric oxygen to form hydroperoxides is hardly measurable, but branched hydrocarbons - especially those with a tertiary carbon atom - are more amenable to self-oxidation. Cumene hydroperoxide is produced by air oxidation of cumene in the benzyl position . This process plays an important role in the industrial production of phenol and acetone from benzene and propene .

properties

Hydroperoxides are unstable compounds that are usually only produced in solution and can only be isolated in substance in exceptional cases. They are mostly volatile and often explosive. For this reason ethers, which can react with atmospheric oxygen according to the above mechanism, must be stored in the absence of light and air. Furthermore, potassium hydroxide pellets are placed in the ether container in order to convert the hydroperoxides formed into the corresponding potassium salts by deprotonation . These are insoluble in the ethereal phase and fall to the bottom, which prevents the simultaneous transfer of hydroperoxide compounds into reaction vessels and the like when ether is removed. The decomposition of hydroperoxides usually also takes place radically.

Hydroperoxides are weakly acidic and form the hydroperoxide ion R – O – O - . As a rule, the salts cannot be isolated.

A qualitative indication of hydroperoxides is based on their oxidative effect. A little potassium iodide is dissolved in glacial acetic acid while warming and a few drops of the substance to be tested are added. If hydroperoxides (or peroxides) are present, the previously colorless solution instantly turns deep brown due to the iodine that forms. The commercially available potassium iodide starch paper (turns deep blue-violet in the presence of oxidizing agents) can also be used for the rapid test. Ether stocks that have been stored for a long time should be checked for their peroxide content in this way before they are used or even distilled. Since the ether hydroperoxides have a higher boiling point than the ether on which they are based, the peroxide content in the residue would rise dangerously during distillation , which can lead to an explosion. Another method for determining hydroperoxides uses the FOX reagent .

use

A technically important hydroperoxide is cumene hydroperoxide , which occurs as a non-isolated intermediate in the synthesis of acetone by the Hock process . The comparatively stable and therefore commercially available tert-butyl hydroperoxide is used for epoxidation in the synthesis laboratory . A particularly well-known application of this type is Sharpless epoxidation .

Individual evidence

  1. ^ Albert Gossauer: Structure and Reactivity of Biomolecules , Verlag Helvetica Chimica Acta, Zurich, 2006, pp. 212-213, ISBN 978-3-906390-29-1 .
  2. ^ Siegfried Hauptmann : Organic Chemistry , 2nd Edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig, 1985, pp. 777-778, ISBN 3-342-00280-8 .
  3. ^ Adalbert Wollrab: Organic Chemistry , Springer Verlag, 2009, 2nd edition, p. 76, ISBN 978-3-642-00780-4 .
  4. ^ Adalbert Wollrab: Organic Chemistry , Springer Verlag, 2009, 2nd edition, p. 78, ISBN 978-3-642-00780-4 .
  5. ↑ Accidents caused by peroxide-forming substances Leaflet of the trade association raw materials and chemical industry , accessed on May 21, 2018.
  6. ^ Siegfried Hauptmann : Organic Chemistry , 2nd edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 334, ISBN 3-342-00280-8 .